Deposition apparatus and deposition method

ABSTRACT

A deposition apparatus according to an exemplary embodiment of the present invention includes a plurality of reactors; a plurality of gas supply units connected to the plurality of reactors; and a plurality of plasma supply units connected to the plurality of reactors. Each of the plasma supply units includes: a plasma power supplier; a plurality of diodes connected to the plasma power supplier; and a reverse voltage driver connected to the plurality of diodes through respectively corresponding switches.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2012-0008739 filed in the Korean IntellectualProperty Office on Jan. 30, 2012, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a deposition apparatus and a depositionmethod.

(b) Description of the Related Art

Recently, many efforts have been made for mass production in asemiconductor process. Particularly, since an atomic layer deposition(ALD) process has a problem of low throughput, a variety of attemptshave been made to overcome that problem. For example, a batch-typechamber was introduced in which a plurality of substrates are mountedvertically. Another type of chamber includes a plurality of single waferprocessing reactors therein. In the latter case, a multi-reactor chamberdeveloped by ASM Genitech Korea Ltd. is released and in usecommercially, and is also disclosed in detail in Korean Patent No.782529. The multi-reactor chamber has a plurality of single waferreactors inside of it, but each of the reactors is individuallycontrolled. Therefore, the multi-reactor chamber can achieve massproductivity and precise control over each substrate, which cannot beachieved in conventional batch-type apparatuses.

Recently, as the critical dimension (CD) of device circuits graduallydecreases, demand for a low temperature process has increased, and muchattention has been paid to a plasma enhanced atomic layer deposition(PEALD) process of which the existing conventional thermal ALD processand a plasma process are combined. The basic patent of the PEALD processhas been described in detail in Korean Patent No. 273473 filed by ASMGenitech Korea Ltd. Recently, in order to accomplish mass production ofthe PEALD process, the plasma process has been applied to themulti-reactor chamber. In general, a radio frequency (RF) generator anda matching box are applied to each reactor one by one. However, aplurality of RF generators and matching boxes that are used lead to highcost. Further, in order to obtain the uniform characteristics during adeposition process performed on a plurality of substrates, plasma powersupplied to each substrate needs to be precisely controlled.

In order to supply plasma power to each reactor, a vacuum relay which iscommercially on sale may be applied. In the case of the vacuum relay,however, the plasma power may not be uniformly supplied, due to a shortlifetime, frequent contact failures and the like.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide a depositionapparatus and a deposition method, which are capable of supplyinguniform RF power to a plurality of individual reactors.

An exemplary embodiment of the present invention provides a depositionapparatus including a plurality of reactors; a plurality of gas supplyunits connected to the plurality of reactors; and a plurality of plasmasupply units connected to the plurality of reactors. Each of the plasmasupply units includes: a plasma power supplier; a plurality of diodesconnected to the plasma power supplier; and a reverse voltage driverconnected to the plurality of diodes through switches, respectively.

The deposition apparatus may further include a plurality of equivalentcircuits connected between the plasma power supplier and the pluralityof diodes, respectively.

The plurality of equivalent circuits may include λ/4 equivalentcircuits, respectively.

The deposition apparatus may further include a channel selectorconfigured to control the connections between the reverse voltage driverand the plurality of diodes.

The channel selector may be driven to alternately connect the reversevoltage driver to the plurality of diodes.

The plurality of reactors may include a first reactor, a second reactor,a third reactor, and a fourth reactor; the plurality of gas supply unitsmay include a first gas supply unit connected to the first and thirdreactors and a second gas supply unit connected to the second and fourthreactors; and the plurality of plasma supply units may include a firstplasma supply unit connected to the first and second reactors and asecond plasma supply unit connected to the third and fourth reactors.

Another exemplary embodiment of the present invention provides adeposition method including steps of: (a) preparing a depositionapparatus including a plurality of reactors including first to fourthreactors, a plurality of gas supply units including a first gas supplyunit connected to the first and third reactors and a second gas supplyunit connected to the second and fourth reactors, and a plurality ofplasma supply units including a first plasma supply unit connected tothe first and second reactors and a second plasma supply unit connectedto the third and fourth reactors; (b) supplying source gas to the firstand third reactors through the first gas supply unit; (c) supplyingreactant gas to the first and third reactors through the first gassupply unit, and supplying source gas to the second and fourth reactorsthrough the second gas supply unit; (d) applying a reverse voltage to afirst diode of the first plasma supply unit connected to the firstreactor to supply plasma power to the first reactor, and applying areverse voltage to a third diode of the second plasma supply unitconnected to the third reactor to supply plasma power to the thirdreactor; (e) supplying source gas to the first and third reactorsthrough the first gas supply unit and supplying reactant gas to thesecond and fourth reactors through the second gas supply unit; and (f)applying a reverse voltage to a second diode of the first plasma supplyunit connected to the second reactor to supply plasma power to thesecond reactor, and applying a reverse voltage to a fourth diode of thesecond plasma supply unit connected to the fourth reactor to supplyplasma power to the fourth reactor.

The reactant gas may include reactive purge gas, and the step (b) mayalso include supplying the reactive purge gas.

The steps (c) to (f) may be repeated a plurality of times.

The method may further include supplying purge gas at one or more ofbetween the steps (b) and (c), between the steps (c) and (d), betweenthe steps (d) and (e), and between the steps (e) and (f).

The reactant gas may include reactive purge gas, and the reactive purgegas may be continuously supplied from the step (c) to the step (f).

The first plasma supply unit may further include a plasma power supplierand first and second equivalent circuits connected between the plasmapower supplier and the first and second diodes, respectively; the secondplasma supply unit may further include third and fourth equivalentcircuits connected between the plasma power supplier and the third andfourth diodes, respectively; and the step (d) may further includeconverting a wavelength of power applied to the plasma power supplierinto λ/4 through the first equivalent circuit before applying thereverse voltage to the first diode, and converting a wavelength of powerapplied to the plasma power supplier into λ/4 through the thirdequivalent circuit before applying the reverse voltage to the thirddiode.

The step (f) may include converting a wavelength of power applied to theplasma power supplier into λ/4 through the second equivalent circuitbefore applying the reverse voltage to the second diode, and convertinga wavelength of power applied to the plasma power supplier into λ/4through the fourth equivalent circuit before applying the reversevoltage to the fourth diode.

According to the exemplary embodiments of the present invention, it ispossible to stably and uniformly supply RF plasma power to a pluralityof individual reactors for a longer time than when an existing vacuumrelay is used. Further, the diodes may be used to implement switchingspeed which is about 40 times faster than that of the existing vacuumrelay, which makes it possible to improve a throughput in the (plasmaenhanced) ALD process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a deposition apparatus according to anexemplary embodiment of the present invention.

FIG. 2 is a circuit diagram of a plasma supply unit of the depositionapparatus according to the exemplary embodiment of the presentinvention.

FIGS. 3A and 3B are graphs showing power switching results of thedeposition apparatus according to experimental examples of the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. As those skilled in the art would realize,the described embodiments may be modified in various different ways, allwithout departing from the spirit or scope of the present invention.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification. It will be understood that whenan element such as a layer, film, region, or substrate is referred to asbeing “on” another element, it can be directly on the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly on” another element, there are nointervening elements present.

Then, referring to FIG. 1, a deposition apparatus according to anexemplary embodiment of the present invention will be described. FIG. 1is a schematic view of the deposition apparatus according to theexemplary embodiment of the present invention.

Referring to FIG. 1, the deposition apparatus according to the exemplaryembodiment of the present invention includes a plurality of reactors R1to R4, a plurality of plasma supply units P1 and P2, and a plurality ofgas supply units G1 and G2. Each of the reactors R1 to R4 may include asubstrate mounted therein, on which a deposition process is to beperformed. The plurality of reactors R1 to R4 includes a first reactorR1, a second reactor R2, a third reactor R3, and a fourth reactor R4.The plurality of plasma supply units P1 and P2 includes a first plasmasupply unit P1 and a second plasma supply unit P2, and the plurality ofgas supply units G1 and G2 includes a first gas supply unit G1 and asecond gas supply unit G2.

FIG. 1 illustrates that the first and second reactors R1 and R2 areconnected to the first plasma supply unit P1, and the third and fourthreactors R3 and R4 are connected to the second plasma supply unit P2.The first and third reactors R1 and R3 are connected to the first gassupply unit G1, and the second and fourth reactors R2 and R4 areconnected to the second gas supply unit G2.

Therefore, the first gas supply unit G1 may supply gas to the first andthird reactors R1 and R3 at the same time, and the second gas supplyunit G2 may supply gas to the second and fourth reactors R2 and R4 atthe same time. Each of the gas supply units G1 and G2 may include a gassupply controller such as a valve, and source gas, reactant gas, andpurge gas may be alternately or selectively supplied to two reactors R1and R3 or R2 and R4 through the gas supply controller.

Further, the first plasma supply unit P1 may supply plasma power to thefirst and second reactors R1 and R2, and the second plasma supply unitP2 may supply plasma power to the third and fourth reactors R3 and R4.

The reactors R1 to R4 are plasma (atomic layer) deposition reactors. Thetype of reactors is not limited, but all types of plasma (atomic layer)deposition reactors may be applied.

Now, referring to FIG. 2, the plasma supply unit of the depositionapparatus according to the exemplary embodiment of the present inventionwill be described. FIG. 2 is a circuit diagram of the plasma supply unitof the deposition apparatus according to the exemplary embodiment of thepresent invention.

Referring to FIG. 2, the plasma supply unit 100 according to theexemplary embodiment of the present invention includes a plasma powersupplier 101 such as an RF power-in port, a plurality of equivalentcircuits 102 a and 102 b connected to the plasma power supplier 101, areverse voltage driver 103, a plurality of diodes 105 a and 105 bconnected to the equivalent circuits 102 a and 102 b, a plurality ofchannels 106 a and 106 b connected to the plurality of diodes 105 a and105 b, a plurality of matching networks 107 a and 107 b connected to theplurality of channels 106 a and 106 b, a channel selector 109 connectedto the reverse voltage driver 103, and a plurality of switches 104 a and104 b for switching between the reverse voltage driver 103 and thechannel selector 109. The channels 106 a and 106 b and the matchingnetworks 107 a and 107 b are connected to reactors 108 a and 108 b,respectively.

The equivalent circuits 102 a and 102 b may be λ/4 equivalent circuits.The λ/4 equivalent circuit converts a wavelength of power supplied fromthe plasma power supplier 101 into λ/4, thereby forming zero or infinite(∞) impedance in each of the channels 106 a and 106 b connected to thediodes 105 a and 105 b.

When a reverse voltage is supplied to any one of the diodes 105 a and105 b through the channel selector 109 connected to the reverse voltagedriver 103, the impedance of the channel 106 a or 106 b connected to thediode 105 a or 105 b becomes ‘0’, and plasma power is supplied to thechannel 106 a or 106 b.

This configuration will be described in more detail. When the channelselector 109 selects the first channel 106 a, the first diode 105 aconnected to the first channel 106 a is connected to the reverse voltagedriver 103 through the first switch 104 a. Therefore, when a reversevoltage is applied to the first diode 105 a from the reverse voltagedriver 103, the first λ/4 equivalent circuit 102 a is non-grounded, andthe impedance of a section from the first λ/4 equivalent circuit 102 ato the first diode 105 a becomes zero. Then, a voltage supplied from theplasma power supplier 101 is transmitted to the first channel 106 a, andthen transmitted to the first reactor 108 a. In this case, since thereverse voltage is not applied to the second diode 105 b connected tothe second channel 106 b, the second λ/4 equivalent circuit 102 b isgrounded, and the impedance of a section from the second λ/4 equivalentcircuit 102 b to the second diode 105 b has an infinite value.Therefore, the voltage supplied from the plasma power supplier 101 isnot transmitted to the second diode 105 b and the second channel 106 b.

Similarly, when the channel selector 109 selects the second channel 106b, the second diode 105 b connected to the second channel 106 b isconnected to the reverse voltage driver 103 through the second switch104 b. Therefore, when a reverse voltage is applied to the second diode105 b from the reverse voltage driver 103, the second λ/4 equivalentcircuit 102 b is non-grounded, and the impedance of the section from thesecond λ/4 equivalent circuit 102 b to the second diode 105 b becomeszero. Then, the voltage supplied from the plasma power supplier 101 istransmitted to the second channel 106 b and then transmitted to thesecond reactor 108 b. In this case, since the reverse voltage is notapplied to the first diode 105 a connected to the first channel 106 a,the first λ/4 equivalent circuit 102 a is grounded, and the impedance ofthe section from the first λ/4 equivalent circuit 102 a to the firstdiode 105 a has an infinite value. Then, the voltage supplied from theplasma power supplier 101 is not transmitted to the first diode 105 aand the first channel 106 a.

The channel selector 109 of the deposition apparatus according to theexemplary embodiment of the present invention determines the impedancestates of the equivalent circuits and the diodes which are connected tothe respective channels, and determines whether or not to transmitplasma power to the respective reactors.

As such, the channel selector 109 may transmit plasma power to a desiredreactor through a desired channel, and the plasma power transmission maybe alternately performed in the respective reactors.

According to the exemplary embodiment of the present invention, thechannel selector 109 selects any one of the two reactors 108 a and 108 bto supply plasma power, but the present invention is not limitedthereto. According to another exemplary embodiment of the presentinvention, the channel selector 109 connected to two or more reactorsmay be applied.

A deposition method of the deposition apparatus according to theexemplary embodiment of the present invention will be described withreference to FIGS. 1 and 2.

At a first step, the first gas supply unit G1 supplies source gas to thefirst and third reactors R1 and R3 at the same time, and the second gassupply unit G2 continuously supplies only reactive purge gas to thesecond and fourth reactors R2 and R4. As the source gas is supplied tothe first and third reactors R1 and R3, source gas molecules areadsorbed onto the substrates mounted in the first and third reactors R1and R3. In this case, the source gas and the reactive purge gas may besupplied together. The reactive purge gas refers to gas which includes acomponent forming a final thin film, but serves as only purge gaswithout reacting with source gas when the reactive purge gas isinactivated, and reacts with the source gas when the reactive purge gasis activated (decomposed) by plasma. For example, N₂ is used as simplepurge gas when inactivated, but used as a nitrogen source for formingnitride when activated by plasma.

At a second step, the supply of the source gas to the first and thirdreactors R1 and R3 is stopped, and the source gas molecules adsorbedonto the substrate and the source gas remaining in the reactors arecontinuously purged by the reactive purge gas. Simultaneously, thesource gas is supplied to the second and fourth reactors R2 and R4through the second gas supply unit G2 at the same time, and the reactivepurge gas may be supplied together.

At a third step, plasma power is supplied to the first and thirdreactors R1 and R3 to which the reactive purge gas is being supplied.Specifically, the first plasma supply unit P1 supplies plasma power tothe first reactor R1, and the second plasma supply unit P2 suppliesplasma power to the third reactor R3. As the reactive purge gas suppliedto the first and third reactors R1 and R3 is activated and decomposed bythe plasma power, the reactive purge gas reacts with the source gasmolecules adsorbed onto the substrate, thereby forming a desired thinfilm.

The supply of the plasma power is performed by the operation of theplasma supply unit 100 described with reference to FIG. 2. That is, thechannel selector 109 of the first plasma supply unit P1 applies areverse voltage to the diode connected to the first reactor R1, and thechannel selector 109 of the second plasma supply unit P2 applies areverse voltage to the diode connected to the third reactor R3. Then,the plasma power is applied to the first and third reactors R1 and R3.

At a fourth step, the supply of the source gas to the second and fourthreactors R2 and R4 is stopped, and the source gas molecules adsorbedonto the substrate and the source gas remaining in the reactors arepurged while only the reactive purge gas is continuously supplied by thesecond gas supply unit G2.

At a fifth step, the first plasma supply unit P1 stops supplying plasmapower to the first reactor R1, and supplies plasma power to the secondreactor R2, and the second plasma supply unit P2 stops supplying plasmapower to the third reactor R3, and supplies plasma power to the fourthreactor R4. Accordingly, as the reactive purge gas supplied to thesecond and fourth reactors R2 and R4 is activated and decomposed, thereactive purge gas reacts with the source gas molecules adsorbed ontothe substrate, thereby forming a desired thin film.

The supply of the plasma power is performed by the operation of theplasma supply unit 100 described with reference to FIG. 2. That is, thechannel selector 109 of the first plasma supply unit P1 stops applying areverse voltage to the diode connected to the first reactor R1, andapplies a reverse voltage to the diode connected to the second reactorR2, and the channel selector 109 of the second plasma supply unit P2stops applying a reverse voltage to the diode connected to the thirdreactor R3, and applies a reverse voltage to the diode connected to thefourth reactor R4. Then, plasma power is applied to the second and thefourth reactors R2 and R4.

In this case, the reactive purge gas may be continuously supplied to thefirst and third reactors R1 and R3. The reactive purge gas supplied tothe first and third reactors R1 and R3 serves only as purge gas and isnot activated any more, because the plasma power is not supplied.Therefore, the reactive purge gas does not chemically react with thethin film which is already adsorbed onto the substrate, but simplypurges only the remaining reactant gas.

At a sixth step, the reactive purge gas and the source gas are suppliedto the first and third reactors R1 and R3 again. Further, the plasmapower supplied to the second and fourth reactors R2 and R4 is stopped,and only the reactive purge gas is supplied to the second and fourthreactors R2 and R4. The reactive purge gas supplied to the second andfourth reactors R2 and R4 is not activated, because the plasma power isnot supplied. Therefore, the reactive purge gas does not chemicallyreact with the thin film which is already adsorbed onto the substrate,but simply purges only the remaining reactant gas.

Then, as the second to sixth steps are repeated, the PEALD process isperformed in the plurality of reactors R1 to R4. The reactive purge gasmay be supplied at the step where the reactant gas is supplied, orcontinuously supplied during the entire steps. The reactive purge gasmay be continuously supplied to minimize a pressure change inside thereactors, which makes it possible to perform a stable process.

In the exemplary embodiment, the deposition process of the first andthird reactors R1 and R3 is started before the deposition process of thesecond and fourth reactors R2 and R4, but the deposition process of thesecond and fourth reactors R2 and R4 may be started before thedeposition process of the first and third reactors R1 and R3.

The deposition apparatus according to the exemplary embodiment includesthe plasma supply unit including the equivalent circuits, the diodes,and the reverse voltage driver. Therefore, the switching time foralternately supplying plasma power to the plurality of reactorsdecreases, and the durability of operation characteristics increases.Therefore, it is possible to solve problems such as a short lifetime andfrequent contact failures which may occur in the method using theconventional vacuum relay. Accordingly, it is possible to implement thePEALD process of which the productivity is enhanced.

Then, referring to FIGS. 3A and 3B, power switching results of thedeposition apparatus according to experimental examples of the presentinvention will be described. FIGS. 3A and 3B are graphs showing thepower switching results obtained from the deposition apparatus accordingto the experimental examples of the present invention. FIG. 3A shows aresult obtained by supplying plasma power to a plurality of reactorsusing the conventional vacuum relay, and FIG. 3B shows a result obtainedby supplying plasma power to the plurality of reactors through theplasma supply unit using the diodes as in the deposition apparatusaccording to the exemplary embodiment of the present invention.

When the conventional vacuum relay is used, the switching time (t1) foreach of the reactors is about 8 msec. However, when the plasma supplyunit using the diodes according to the exemplary embodiment of thepresent invention is used, the switching time (t2) is 200 μsec. It canbe seen that the switching time of the deposition apparatus according tothe exemplary embodiment of the present invention becomes about 40 timesshorter than the switching time of the conventional depositionapparatus.

As such, the deposition apparatus according to the exemplary embodimentof the present invention includes the plasma supply unit including theequivalent circuits, the diodes, and the reverse voltage driver.Therefore, the switching time for alternately supplying plasma power tothe plurality of reactors decreases while the durability of theoperation characteristic increases. Accordingly, it is possible to solveproblems such as a short lifetime and frequent contact failures whichmay occur in the method using the conventional vacuum relay. As aresult, it is possible to implement the PEALD process of whichproductivity is enhanced.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosed exemplaryembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A deposition apparatus comprising: a plurality ofreactors; a plurality of gas supply units connected to the plurality ofreactors; and a plurality of plasma supply units connected to theplurality of reactors, wherein each of the plurality of plasma supplyunits comprises: a plasma power supplier; a plurality of diodesconnected to the plasma power supplier; and a reverse voltage driverconnected to the plurality of diodes through respectively correspondingswitches.
 2. The deposition apparatus of claim 1, further comprising: aplurality of equivalent circuits connected between the plasma powersupplier and the plurality of diodes.
 3. The deposition apparatus ofclaim 2, wherein: the plurality of equivalent circuits comprise λ/4equivalent circuits.
 4. The deposition apparatus of claim 2, furthercomprising: a channel selector configured to control the connectionsbetween the reverse voltage driver and the plurality of diodes.
 5. Thedeposition apparatus of claim 4, wherein: the channel selector is drivento alternately connect the reverse voltage driver to the plurality ofdiodes.
 6. The deposition apparatus of claim 1, further comprising: achannel selector configured to control the connections between thereverse voltage driver and the plurality of diodes.
 7. The depositionapparatus of claim 6, wherein: the channel selector is driven toalternately connect the reverse voltage driver to the plurality ofdiodes.
 8. The deposition apparatus of claim 1, wherein: the pluralityof reactors comprise a first reactor, a second reactor, a third reactor,and a fourth reactor; the plurality of gas supply units comprise a firstgas supply unit connected to the first and third reactors and a secondgas supply unit connected to the second and fourth reactors; and theplurality of plasma supply units comprise a first plasma supply unitconnected to the first and second reactors and a second plasma supplyunit connected to the third and fourth reactors.
 9. A plasma enhancedatomic layer deposition (PEALD) method using a plurality of reactors,the method comprising the steps of: (a) preparing a deposition apparatusincluding a plurality of reactors including first to fourth reactors, aplurality of gas supply units including a first gas supply unitconnected to the first and third reactors and a second gas supply unitconnected to the second and fourth reactors, and a plurality of plasmasupply units including a first plasma supply unit connected to the firstand second reactors and a second plasma supply unit connected to thethird and fourth reactors; (b) supplying source gas to the first andthird reactors through the first gas supply unit; (c) supplying reactantgas to the first and third reactors through the first gas supply unit,and supplying source gas to the second and fourth reactors through thesecond gas supply unit; (d) applying a reverse voltage to a first diodeof the first plasma supply unit connected to the first reactor to supplyplasma power to the first reactor, and applying a reverse voltage to athird diode of the second plasma supply unit connected to the thirdreactor to supply plasma power to the third reactor; (e) supplyingsource gas to the first and third reactors through the first gas supplyunit and supplying reactant gas to the second and fourth reactorsthrough the second gas supply unit; and (f) applying a reverse voltageto a second diode of the first plasma supply unit connected to thesecond reactor to supply plasma power to the second reactor, andapplying a reverse voltage to a fourth diode of the second plasma supplyunit connected to the fourth reactor to supply plasma power to thefourth reactor.
 10. The method of claim 9, wherein: the reactant gascomprises reactive purge gas, and the step (b) comprises furthersupplying the reactive purge gas together with the source gas.
 11. Themethod of claim 10, wherein: the steps (c) to (f) are repeated aplurality of times.
 12. The method of claim 9, wherein: the steps (c) to(f) are repeated a plurality of times.
 13. The method of claim 9,further comprising: supplying purge gas at one or more of between thesteps (b) and (c), between the steps (c) and (d), between the steps (d)and (e), and between the steps (e) and (f).
 14. The method of claim 9,wherein: the reactant gas comprises reactive purge gas, and the reactivepurge gas is continuously supplied from the step (b) to the step (f).15. The method of claim 9, wherein: the first plasma supply unit furthercomprises a plasma power supplier and first and second equivalentcircuits connected between the plasma power supplier and the first andsecond diodes, respectively; the second plasma supply unit furthercomprises third and fourth equivalent circuits connected between theplasma power supplier and the third and fourth diodes, respectively; andthe step (d) comprises converting a wavelength of power applied to theplasma power supplier into λ/4 through the first equivalent circuitbefore applying the reverse voltage to the first diode, and converting awavelength of power applied to the plasma power supplier into λ/4through the third equivalent circuit before applying the reverse voltageto the third diode.
 16. The method of claim 15, wherein: the step (f)comprises converting a wavelength of power applied to the plasma powersupplier into λ/4 through the second equivalent circuit before applyingthe reverse voltage to the second diode, and converting a wavelength ofpower applied to the plasma power supplier into λ/4 through the fourthequivalent circuit before applying the reverse voltage to the fourthdiode.